When a rainstorm swept over the scorched hillsides left by the 2022 McKinney Fire, it seemed like relief was finally arriving. Instead, dissolved oxygen in the Klamath River collapsed to zero \u2014 and stayed there for more than five hours. Fish died along nearly 60 miles of one of California\u2019s most culturally significant waterways.<\/p>\n
Rain was supposed to help. A new USGS study, the first of its kind, documents how it didn\u2019t.<\/p>\n
A storm that made things worse<\/p>\n
The McKinney Fire ignited in late July 2022 in Siskiyou County, becoming the largest wildfire in California that year. It left thousands of acres of scorched hillslopes \u2014 bare, unstable ground with little vegetation to slow runoff. When a high-intensity rainstorm followed, water moved fast across that burned landscape, picking up everything in its path.<\/p>\n
What it carried into the Klamath River was devastating. Stormwater flushed ash, charcoal, and sediment from the fire scar directly into the waterway. Dissolved oxygen dropped to zero \u2014 a condition scientists call anoxia \u2014 and held there for more than five hours. Fish had no way to survive it. Aquatic life died along nearly 60 miles of river, including juvenile salmon already navigating one of the most challenging migration corridors in the American West.<\/p>\n
How fire scars turn rain into a threat<\/p>\n
The damage didn\u2019t happen all at once. According to the USGS study, the event unfolded in two distinct waves: an initial flood surge that moved quickly downstream, then a second, more dangerous pulse \u2014 a concentrated load of ash, charcoal, and sediment scraped from freshly burned hillslopes.<\/p>\n
That organic material doesn\u2019t just cloud the water. As it decomposes, it consumes dissolved oxygen, stripping the river of what fish need to breathe. The more material that enters, the faster oxygen disappears.<\/p>\n
Vegetated hillslopes absorb and filter runoff. Burned ones don\u2019t \u2014 they produce far more extreme runoff and deliver far more oxygen-consuming material in a single event. That\u2019s what makes rain-on-wildfire collisions so dangerous, and so different from typical flood events. This study is the first published research to directly link such an event to lethal water-quality conditions in a large river.<\/p>\n
Sensors that caught what the eye could not<\/p>\n
No one watching the Klamath River that day would have seen the oxygen disappear. The water looked bad \u2014 turbid, dark with ash \u2014 but the invisible collapse of dissolved oxygen required instruments to detect.<\/p>\n
Continuous, high-frequency monitoring sensors made the documentation possible. Stations along the river tracked turbidity, dissolved oxygen, pH, conductivity, and temperature across the full arc of the event. That real-time data let scientists reconstruct exactly what happened and when \u2014 something eyewitness observation alone never could have captured.<\/p>\n
Those stations weren\u2019t operated by USGS alone. The Karuk Tribe and the Yurok Tribe jointly ran monitoring infrastructure alongside federal scientists. Researchers suggest the scarcity of documented post-wildfire anoxia events likely reflects a monitoring gap rather than a rarity of occurrence. Without continuous sensors already in place, events like this simply go unrecorded.<\/p>\n
A river at the center of a culture<\/p>\n
The Klamath River is not just a waterway. For the Karuk and Yurok Tribes, it\u2019s a living system tied to identity, food sovereignty, and generations of ecological stewardship. Salmon are central to both cultures \u2014 and both Tribes have long understood that the river\u2019s health is inseparable from their own.<\/p>\n
Toz Soto, Fisheries Program Manager for the Karuk Tribe Department of Natural Resources, noted that fire frequency, size, and burn intensity are all increasing \u2014 making it more urgent to understand the risks to native fish populations and water quality. The Karuk Tribe, he said, is committed to long-term water-quality monitoring to keep learning about large fires and floods.<\/p>\n
Yurok Tribe Environmental Department Water Program Manager Josh Cahill echoed that commitment. Through the partnership with USGS, he said, the Tribes can track the Klamath River\u2019s ever-changing conditions in real time.<\/p>\n
What comes next as wildfires intensify<\/p>\n
The conditions that produced this event are becoming more common. Wildfires across the western United States are growing more frequent and more severe<\/a>, while late-summer monsoon storms are intensifying \u2014 raising the probability that the two will collide over freshly burned land.<\/p>\n